Conventionally, a method of ascertaining a timing at which consumable parts such as a discharge tube, oscillation lamp and the like of a laser beam oscillator must be replaced is such that consumed parts are replaced with new parts when these consumable parts completely fail and the laser beam oscillator cannot be operated or when an operation time predetermined to each of the consumable parts has elapsed.
Nevertheless, when the operation of the laser beam oscillator has actually stopped, it is not always caused by the consumption of the discharge tube, oscillation lamp and the like. Therefore, the method of replacing parts after the laser beam oscillator cannot be operated has a problem in that a job for investigating the reason why the oscillator is stopped needs considerable labor and the recovery thereof requires a long time.
Further, a degree of consumption of parts changes depending upon a laser beam output therefrom even if they are operated for the same time. Consequently, in the method of replacing parts after they have been operated for a predetermined time, there is a possibility that parts which are still sufficiently usable may be discarded.